Optical fibres with or without tunability are used in a wide range of technical areas, such as optical communication, sensor technologies, imaging, lithography, opto-medical systems, material processing and so forth.
It is desirable to be able to shape the spectral properties for the light propagation of such a fibre and if possible on a short time scale and for a number of different wave-lengths. This applies both to continuous wave systems and pulsed wave systems.
For optical communication, for example, it is desirable to be able to send signals at a high bit rate over long distances. This requires short light pulses of high intensity and fibres with little or no pulse distortion due to for instance dispersion or non-linear effects. As communication over the years has developed towards higher bit rates, there is a continuous need for improving properties of fibres, such as being able to shape the transmission spectrum of the fibre and/or tune the transmission properties of the fibre, such as the polarisation of light propagating through the fibre.
Within the last couple of years a new type of optical fibre has shown the ability to guide light in a core surrounded by microstructured elements, which are elongated in the longitudinal direction of the fibre. These fibres are amongst others known as photonic crystal fibres, photonic bandgap fibres and holey fibres.
US 2005/0169590 discloses an optical fibre, which comprises a core region and a microstructured cladding region surrounding the core region. The cladding region includes a number of cladding elements or air holes, said cladding elements being arranged in a two-dimensional periodic manner or a Bragg-type of manner. At least a number of the cladding elements are filled in at least one longitudinally extending section of the optical fibre with a liquid crystal material. This section exhibits a photonic bandgap effect for at least one phase state of the liquid crystal. The optical properties of the crystal fibre can be changed by use of for instance heating means or electrooptical means. Thereby it is possible to change the spectral transmission bands of the optical fibre.
EP patent application EP 05388109 discloses an optical fibre of the photonic bandgap type, wherein the fibre comprises a transition region, in which the fibre is tapered or otherwise shaped in order to shape the transmission spectrum of the fibre. At least a part of the transition region is filled with or consists of a high refractive index material, such as liquid crystal, which is sensitive to external influences, such as thermal influences or electrical fields. Thereby, it is possible to tune the transmission spectrum of the fibre by use of thermal or electrical means.
EP patent application EP 05388110 discloses an optical fibre of the photonic bandgap type, wherein the fibre comprises a number of first cladding elements with a first cross-sectional dimension and at least one second cladding element with a second cross-sectional dimension, wherein the first cross-sectional dimension and the second cross-sectional dimension are different. This introduces a defect to the lattice structure of the cladding elements, in which pseudo-surface modes can propagate, and in effect a notch-filter can be obtained. Along at least a part of the longitudinal direction of the fibre, said cladding elements are filled with or consist of a high refractive index material, such as liquid crystal, which are sensitive to external influences, such as thermal influences or electrical fields. Thereby, it is possible to tune the transmission spectrum of the fibre by use of thermal or electrical means.
“Fiber-optic switch”, J. D. Crow, IBM Technical Bulletin, Vol. 21, no. 11, April 1979, page 4686, XP002379775, discloses a fibre-optic switch comprising a first substrate made of silicon and having a first groove. A second mating substrate with a second groove is placed on top of the first substrate. The second groove has two electrodes and when a potential is applied between the two electrodes forming an electric field there between, the end of an input fibre positions itself in the second groove. When the field is removed by turning off the applied voltage, the natural elasticity of the fibre causes it to relax to a position against the first groove. Two output fibres are positioned in the grooves with their end faces very close to the two alternative positions of the input fibre, thereby being able to collect the light from the input fibre.
All the aforementioned photonic bandgap fibres have a need for a simple and inexpensive package and/or actuator means for tuning the transmission properties of the fibre.